As for a wildfire...
Most basement roofs are the wooden floor of the main level above it. If you're in the basement and the house goes, you go too. No escaping that.
I've seen plenty of video and photo evidence of the fire destruction out west (similar to bad house fire here). The entire house burns and everything falls into the basement/crawl space.
It's a death trap in a fire. That's why you can't have legal living space in a basement without external egress windows or stairs other than the one staircase coming down from the main level. You can't advertise a house with 4 bedrooms if one or more of the bedrooms is in a basement without egress.
Fortunately, egress windows/stairs are very easy to install in new construction, and also very easy to retrofit in old construction basements. They make pre-cast units or you can form and pour your own.
But my main concern with trying to ride out a wildfire in a basement, even a solid concrete bunker, would be lack of air. You'd probably get asphyxiated by the smoke, and, depending on the length of the fire, maybe the heat?
The WWII bunkers had plans for external air vents and a hand crank unit that pulled the air through a series of dry oil filters. That would trap any radioactive particles in the oil filter medium so you wouldn't breath them in. I'd imagine you could do something similar for fire smoke.
However, if there's a wildfire, and you have advanced notice, I'd just get the heck out. Not worth risking it in an untried system.
